Reduce non-serializable assignableAttributes

[bemky]

Problem

The assignableAttributes system supports non-serializable types (objects, arrays, functions) via a _ref manifest pattern — generating ref IDs, storing values in a global KompElement.manifest Map, writing opaque foo_ref="komp-ref-42" attributes to the DOM, and using a FinalizationRegistry for cleanup. This is complex and unconventional.

Since the primary use case is programmatic (new Dropdown({anchor: el})), most non-serializable values don't need DOM representation. Many can be replaced with serializable alternatives, events, or removed from the public API entirely.

Audit

27 non-serializable attributes found across the library:

Callbacks — replace with events

These are function attributes that duplicate what addEventListener already does.

Component	Attribute	Description	Alternative
Floater	onShow	Called when floater becomes visible	Already fires shown event — remove attribute
Floater	onHide	Called when floater hides	Already fires hidden event — remove attribute
ContentArea	onchange	Called on blur after content edited	Fire a change event with {detail: {value, oldValue}}
Dropzone	onFileDrop	Called per file dropped	Already fires filedrop event — remove attribute

Transform/render functions

These define how something renders or transforms data.

Component	Attribute	Description	Alternative
Input	dump	Transforms input value before storing to target	String key into a named-transforms registry (e.g. "number", "date")
Input	load	Transforms target value for display	Same registry approach
Select	dump	Transforms selected value before storing	Same as Input
Select	load	Transforms target value for display	Same as Input
SearchField	search	Async function performing the search	URL string — component fetches and parses JSON
SearchField	result	Renders a single result item	HTML template string with ${field} interpolation
SearchField	input	Factory for the input element	Object config passed to createElement
SearchField	empty	Content when no results (when fn)	Already supports string — drop function variant
SearchField	loader	Content while loading (when fn)	Already supports string — drop function variant
Resizer	bounds	Returns {top,right,bottom,left} constraints	JSON object or keyword string ("parent", "viewport")
TableColumn	header	Renders header cell (when fn)	Already supports string — sufficient
TableColumn	render	Renders cell content	Template string with field interpolation
SpreadsheetColumn	input	Factory for the edit input element	String type key looked up in a registry
SpreadsheetColumn	copy	Converts cell value to clipboard format	Built-in default covers most cases
SpreadsheetColumn	paste	Converts clipboard data to cell value	Same as copy

Internal object references — remove from public API

These are parent-child references passed during construction. They shouldn't be assignableAttributes at all — they're internal wiring.

Component	Attribute	Description	Alternative
Input	target	Data object to bind input value to	Pass internally, remove from public API
Select	target	Data object to bind selection to	Same as Input
TableRow	table	Ref to parent Table	this.closest('komp-table') or parent injection
TableCell	table	Ref to parent Table	Same — DOM traversal or parent injection
TableCell	column	Ref to TableColumn config	Column index (number) + lookup from table
TableCell	record	Data row (when fn)	Already supports plain object — drop function variant

Already handled well

• Floater anchor — has a load() that resolves selector strings
• Floater container — already accepts strings

Recommendations

1. Callbacks (4): Remove — all redundant with existing events
2. Internal references (6): Remove from public assignableAttributes, use DOM traversal or internal injection
3. Transform/render functions (15): Consider a registry + template string approach for common cases, keep programmatic escape hatch
4. Simplify the ref system: Once the above are addressed, evaluate whether the manifest/FinalizationRegistry/_ref pattern is still needed